1. Field of the Invention
The present invention relates to lead shielding with cooling air guidance for a betatron, particularly for use in an x-ray inspection system.
2. Description of the Background Art
X-ray inspection systems such as the one illustrated in FIG. 4 are used, as is well-known, in the inspection of large-volume articles such as containers and motor vehicles for illegal contents such as weapons, explosives, or contraband goods. In so doing, x-radiation is produced and directed at the article (e.g., target 50). The x-radiation attenuated by the object is measured by means of a detector (e.g., x-ray detector 52) and analyzed by an evaluation unit (e.g., evaluation unit 54). Therefore, a conclusion can be reached on the nature of the object. This type of x-ray inspection system is known, for example, from European Pat. No. EP 0 412 190 B1, which corresponds to U.S. Pat. No. 5,065,418.
Betatrons are used to generate x-radiation with the energy of more than 1 MeV needed for the inspection. These are circular accelerators in which electrons are accelerated in an orbit. The accelerated electrons are guided onto a target, where upon impacting they produce Bremsstrahlung whose spectrum depends, inter alia, on the energy of the electrons.
A betatron disclosed in Offenlegungsschrift [Unexamined German Pat. Application] No. DE 23 57 126 A1 consists of a two-part inner yoke, in which the front sides of both inner yoke parts face each other spaced apart. A magnetic field is produced in the inner yoke by means of two main field coils. An outer yoke connects the two inner yoke part ends distant from one another and closes the magnetic circuit.
An evacuated betatron tube, in which the electrons to be accelerated circulate, is arranged between the front sides of the two inner yoke parts. The front sides of the inner yoke parts are formed in such a way that the magnetic field produced by the main field coil forces the electrons into a circular orbit and moreover focuses them onto the plane in which this orbit lies. To control the magnetic flux, it is prior in the art to arrange a ferromagnetic insert between the front sides of the inner yoke parts within the betatron tube.